The realization of high-yield, low-threshold carrier multiplication (CM) in semiconductor quantum dots (QDs) and other types of nanomaterials (e.g., semiconductor nanorods and carbon nanotubes) is a promising step toward next generation solar cells with performance beyond the Shockley-Queisser limit. Recent studies of QD solar cells have shown that CM can indeed produce greater-than-unity quantum efficiencies in photon-to-charge-carrier conversion, establishing the relevance of this process to practical photovoltaics (PVs). While being appreciable, the reported CM yields are still well below the energy-conservation-defined limit required for a significant increase in the PV power-conversion efficiency over traditional bulk materials. At present, the design of nanomaterials with improved CM is hindered by a poor understanding of the mechanism underlying this process. Here we present a possible solution to this problem by introducing a phenomenological model, which treats CM as a competition between impact-ionization-like scattering and non-CM energy losses. Importantly, it allows for evaluation of expected CM yields from fairly straightforward measurements of Auger recombination (inverse of CM) and near-band-edge carrier cooling. The validation of this model via a comparative CM study of PbTe, PbSe and PbS QDs suggests that it indeed represents a predictive capability, which might help in the development of nanomaterials with improved CM performance.

Carrier multiplication in semiconductor nanocrystals within the framework of two competing energy relaxation mechanisms

246th National Meeting (2013)

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